The recent increase in the panel size and resolution of LCD (liquid crystal display) panels has caused a problem of the increase in the power consumption. One approach for suppressing the power consumption is to decrease the brightness of the backlight. However, the decrease in the brightness of the backlight undesirably causes a problem that the display quality is deteriorated due to the insufficient contrast for images with reduced brightness.
One approach for reducing the brightness of the backlight without deterioration of the display quality is to perform a correction calculation such as the gamma correction on input image data for emphasizing the contrast. In this operation, controlling the brightness of the backlight together with performing the correction calculation allows further suppressing the deterioration in the image quality.
In view of such background, the inventors have proposed a technique in which a correction calculation based on a calculation expression is performed on input image data (for example, Japanese Patent Gazette No. 4,198,720 B). In this technique, the correction calculation is performed using a calculation expression in which the input image data are defined as a variable and coefficients are determined on the basis of correction point data. Here, the correction point data define a relation of the input image data to corrected image data (output image data); the correction point data are determined depending on the APL (average picture level) of the image to be displayed or the histogram of the grayscale levels of respective pixels in the image.
Also, Japanese Patent Application Publication No. H07-281633 A discloses a technique for controlling the contrast by determining a gamma value on the basis of the APL of the image to be displayed and the variance (or standard deviation) of the brightnesses of pixels and performing a gamma correction by using the determined gamma value.
Moreover, Japanese Patent Application Publication No. 2010-113052 A discloses a technique for decreasing the power consumption with reduced deterioration of the image quality, in which an extension process (that is, a process of multiplying the grayscale levels by β(where 1 <β<2)) is performed on display data while the backlight brightness is reduced. The extension process disclosed in this patent document is a sort of correction calculation performed on the input image data.
Although the above-described correction calculation is effective for improving the image quality, these patent documents are silent on a problem which may occur in the case that a technique of performing a correction calculation on input image data is applied to a display device which incorporates a plurality of display panel drivers to drive the display panel (for example, display devices applied to mobile terminals which include a large display panel, such as tablets). According to a study of the inventors, a problem related to the necessary data transmission rate and cost may occur, when the technique for performing a correction calculation on the input image data is applied to a display device which includes a plurality of display panel drivers to drive a display panel.